The hyperdense crescent sign

摘要

The hyperdense crescent sign The hyperdense or high-attenuation crescent sign describes the presence of a crescent-shaped accumulation of blood within an intraluminal thrombus or the wall of an aortic aneurysm (Fig. 1) [1, 2]. This sign was first described by Mehard et al. and is best seen on unenhanced CT images, but can also be seen on contrast-enhanced images [1]. The acute hematoma appears hyperdense on unenhanced CT images due to the penetration of fresh blood inside the mural thrombus and within the aortic wall, taking the shape of the French pastry, "le croissant" and resembling a crescent moon (Fig. 2). This sign is considered a sign of aneurysm instability and "impending" rupture [1, 3]. Detecting the impending signs of rupture ("contained rupture") is important, as aortic aneurysm rupture has a very high mortality rate with an estimated 15,000 to 30,000 yearly deaths in the United States [4]. This sign differs from the "draped aorta" sign, a sign of contained rupture, where there is loss of the interface between the aortic wall and adjacent structures [5].